Poison hemlock has sprouted up in almost every state this year. What do you do if your pet comes in contact with it?

It's always scary when a weed that shows up in nearly every state in the country is both beautiful and dangerous. News out of the Midwest is that this year's cool, wet weather has helped poison hemlock during its growing season of late June to August to spread from roadside fields and ditches to more populated areas. And this Queen Anne's lace lookalike contains dangerous neurotoxins, which, if ingested, can harm humans, livestock, and pets.

"It just hit this exponential rate of spread," Dan Shaver with Indiana's Natural Resources Conservation Service recently told the Indianapolis Star. "Poison hemlock was nowhere and all of a sudden it was everywhere."

The plant's beautiful cluster of tiny white flowers on top of large stems should be a warning sign to stay away, for both people and pets.

What Is Poison Hemlock and Where Does It Grow?

Poison hemlock (Conium maculatum) sounded like a good idea at the time back in the 1800s, when it was brought into American gardens from Europe and Asia and marketed as a pretty "winter fern." But it didn't stay in gardens and since has poked up in fields, farms, and in the wild all over the country.

Poison hemlock, a biennial plant in full bloom in summer, is marked by umbrella-shaped clusters of small white flowers at the end of every stem, like the lookalike plant Queen Anne's lace. You can see the similarities and subtle differences in the U.S. Fish and Wildlife Service's plants to avoid guide. Both of those plants show up there because Queen Anne's lace is also toxic for pets, Schmid says.

What differentiates poison hemlock is a bigger stem with purple splotches along the stalk. In addition to Queen Anne's lace, poison hemlock or its roots can be confused with wild carrot and wild parsnip. But those don't have the purple-splotched, hairless stems of poison hemlock.

Because poison hemlock loves shaded areas with moist soil, it commonly pops up in meadows, marshes, and low-lying areas. But a nice, shaded, untended urban corner or undeveloped field with trees in wet weather could see blooms in the summer.

If you're worried about animals and poisonous weeds, it's not the only hemlock to worry about, says Renee Schmid, DVM, DABVT, DABT, a veterinarian toxicologist who works with Pet Poison Helpline. The even more poisonous water hemlock is also a danger, she says.

poison hemlock dangers for dogs
Credit: Feifei Cui-Paoluzzo / Getty

Is Poison Hemlock Toxic to Dogs?

Poison hemlock is toxic, when ingested, to people, livestock and, yes, cats and dogs. However, only livestock, who may get it mixed up with hay or eat it in large amounts in a field, are likely to eat enough to cause severe poisoning, Schmid says.

"Over the last five years, Pet Poison Helpline has only received 19 calls for potential exposure to poison hemlock, and that's very few," she says. "It's more of a problem with grazing animals like cattle or horses as opposed to a few nibbles once or twice from a dog or cat."

That said, every part of poison hemlock, from stem to flowers, contains a neurotoxin that can cause serious problems if eaten in large quantity.

"It's somewhat similar to nicotine," Schmid says. "It causes an initial excitement in an animal, then depression. That can lead to paralysis of the respiratory muscles with large ingestions."

Enough poison hemlock ingested or a more extreme reaction could all lead to a dangerous poisoning that could require a visit to the veterinary clinic.

Signs of Poison Hemlock Toxicity in Dogs

Your dog might be the pooch who loves to chew leaves, flowers, and wild things in the house, in the yard, and on walks. You're probably familiar with some other dangerous plants already. If you think your pet has ingested poison hemlock, there are signs to watch for that could necessitate a call to a poison hotline or your veterinary practice, according to Schmid:

  • Gastrointestinal upset
  • Vomiting
  • Excitation followed by weakness and depression
  • In worst-case scenarios, coma-like signs and significant respiratory distress, or shallow or difficult breathing.

"Again, these would not be common with a small one-time exposure," Schmid says.

If It's called for, depending on signs and severity, veterinarians at the hospital can safely induce vomiting or defecation and offer breathing help in extreme cases. Owners of pets who may have eaten poison hemlock should watch for the signs and call the veterinarian if they see them.

How to Get Rid of Poison Hemlock in Your Yard

Owners of livestock tend to keep a sharp eye out for poison hemlock. If pregnant animals eat too much, bone or growth deformities can show up in foals, calves, piglets, and other newborns. That means most of the fighting to make sure poison hemlock is gone is a farm and field problem.

But what if you see poison hemlock in your neighborhood, local dog park, or favorite hiking trail? Take the time to reach out to property owners when you can to let them know they've got an infestation.

What if the poison hemlock is on your own property? The USDA offers advice to agriculturalists in the Southwest that may help anyone. If you're cutting or removing the blooming plants, wearing gloves is recommended. Don't mow over poison hemlock, as the seeds will remain in the ground and be spread wherever else you mow. And don't expect, even with herbicides and removal, that poison hemlock won't be back next season. It might take a season or two to get rid of all those seeds hiding in the soil.

If you've never faced off with poison hemlock in your yard, consider contacting your local USDA or college with extension courses on local plants. Unfortunately, poison hemlock can show up almost anywhere in the country with the right conditions, so local plant experts should have good advice for getting rid of it in your area.

Overall, don't panic! Keep your pets (and any kids who think the flowers are pretty enough to play with) supervised and clear of anything that looks like poison hemlock, and it likely won't be a problem.